A machine tool includes a metal housing formed with a through hole, a shaft, and a bearing sleeved on the shaft. A conventional sensor is disposed in the machine tool and includes a sensor module and a battery for supplying electrical energy to the conventional sensor. The sensor module is utilized to sense states of the shaft and the bearing of the machine tool for generating a sensor output, which is transmitted via a transmission line that is electrically connected to the conventional sensor and that passes through the through hole to a receiving device external to the machine tool.
Due to the shielding effect caused by the metal housing, the conventional sensor cannot be wirelessly powered by electrical energy from outside of the machine tool, so the battery is required to be disposed in the machine tool. However, the battery has limited battery capacity, and replacing the battery inside the machine tool when the battery runs down proves to be a troublesome task. In addition, formation of the through hole in the metal housing may incur a higher manufacturing cost and reduce the service life of the machine tool. Moreover, in order to connect the conventional sensor and the receiving device with the transmission line, a relatively complicated design should be considered for the wiring of the conventional sensor, causing limited choices in terms of placement of the conventional sensor.